Medicinal aerosol inhalers are commonly used to treat a number of medical conditions. It is well known that medicinal aerosols, whether they originate from a metered dose inhaler (MDI), dry powder inhaler (DPI), or a nebulizer, consist of a distribution of particles with varying sizes. For a particle to be considered respirable, meaning it will have a high probability of depositing in the lung upon inhalation, it should have an aerodynamic diameter of less than about 4.7 micrometers. Larger, non-respirable particles can be deposited in a patient's mouth and/or throat, which can lead to undesirable effects. Mouth and/or throat deposition can lead to a displeasing taste, as well as potentially causing side effects related to drug dosing by a non-inhalation route. It is thus desirable to provide an aerosol dose to a patient that consists primarily or entirely of respirable particles, that is, a dose that has a high respirable fraction.
In the development and manufacture of medicinal aerosol formulations, however, there are many factors that need to be taken into consideration, for example, drug solubility and/or stability in a suitable medium, the ability to prepare small particles, and the necessary dosage. Oftentimes, it is not possible or practical to make a medicinal aerosol where all of the particles delivered by a conventional device are respirable. A number of efforts have been made to develop spacers or actuators that provide either a longer or more tortuous path between the formulation reservoir and the patient to either remove non-respirable material or disperse larger aggregates into smaller particles. Medicinal inhaler spacers have incorporated additional distance and/or various configurations of baffles as a method for removal of non-respirable particles (U.S. Pat. No. 5,676,130, Gupte et al.; WO 92/04066, Bisgaard). Rotational motion of an airflow stream has also been proposed (U.S. Pat. No. 6,073,629, Hardy et al.) and in particular airflows described as cyclonic wherein the airflow travels from inlet to outlet by spiraling in one direction along a central axis (U.S. Pat. No. 5,476,093,Lankinen; WO 01/00262, Hamer et al.).